This application includes two sets of experiments which examine quite different aspects of the structure and development of the visual system. One is a continuation of on-going studies of the organization of the dorsal lateral geniculate nucleus in the cat. In adult cats retinal axons and cells in the dorsal lateral geniculate nucleus are filled with horseradish peroxidase. The patterns of synaptic contacts between labeled axons and cells are then analyzed, first using a computerized microscope system (Neuron Tracing System, Eutectic Electronics). This quantitative, 3-dimensional light microscopic analysis will determine the frequency with which single axons contact single cells; how many axons contact a single cell; and the location of these synaptic contacts on the dendritic arbors of the lateral geniculate neurons. The sections are then prepared for electron microscopy to examine the apparent synaptic contacts seen with the light microscope. In parallel experiments, the same techniques will be used to study the postnatal development of these patterns of connections. These results will add to our understanding of the morphological basis for the precise specificity in the functional organization f the visual system. They will also provide new information regarding the developmental process by which this specificity is established. The second set of experiments utilizes culture of embryonic chick retina to study the roles of different adhesion molecules in retinal histogenesis. Retinal explant are taken from six day old embryos at which age the retinal layers are undifferentiated. Within 4 days in culture all of the retinal layers form and our preliminary studies show that cell division ad migration continue in patterns nearly identical to those in the animal. The similarities between development in vitro and in ovo will be compared further. Antibodies to specific retinal cell types will be used to determine if these cell types develop normally in culture. The roles of different adhesion molecules in histogenesis, especially laminin and its receptors, will be assessed by adding antibodies to some of these molecules to the culture medium and testing their effects on different aspects of histogenesis (mitosis, migration and cell differentiation). These results will provide important new information about the specific roles of individual adhesive molecules in the development of the nervous system.